"alan_m" wrote in message
...
During normal operation these types of camera record continuously to the
sd card and when the recording gets to the end of the card it starts at
the beginning overwriting the most historic data.

Until..... you have an accident or more likely the camera falls off the
screen or you jolt the car by driving into a pothole etc. This triggers
the cameras inbuilt accident detection mechanism which then writes
protects the last x minutes of recording on the sd card.

The next time the camera is used, or continues to be used, the normal
recording of video to the sd card takes place until it meets the
section/file which is write protected. At this point the recording will
stop and maybe the cause of your freeze.

Our dashcam (Transcend Drivepro 220) has two folders: one for the circular
writing of the last n hours, and another for protected files that are
triggered by sudden motion detection and which record 30 seconds before and
30 seconds after the trigger point (to give the lead up to and the aftermath
of the collision). The normal circular writing can only overwrite files in
its own folder; the ones in the protected folder accumulate and gradually
use up the SD card space.

Every few months I take the card out of the camera and manually delete any
files in the protected folder apart from ones we want to keep which I copy
to a computer.

There is also a red button on the camera so a passenger can trigger the
writing to the protected folder manually, separate from motion detection.



I would look at type/size of SD card. Our Transcend is happy with up to (I
think) 64 GB cards but not 128 or larger. 64 covers the last few hours
driving: I think we worked out that it would cover one return journey to
work for my wife, so if there was anything we wanted to examine that was
*not* in the protected folder, we needed to look at it that evening or else
it would be overwritten by the following day's journey to work. I bought a
128 GB card and found that the camera wrote fine to it for about an hour but
then it errored. It failed when it had used much less than the 64 GB of a
card that worked.